1. Field of the Invention
This invention relates to a vehicle-carried navigation system for displaying thereon a condition of movement of an automobile such as a current position, a locus of travel, and an advancing direction.
2. Description of the Prior Art
A vehicle-carried navigation system of the type mentioned is already known and disclosed, for example, in Japanese Patent Laid-Open Application No. 61-56910. FIG. 5 shows an exemplary one of such conventional vehicle-carried navigation systems.
Referring to FIG. 5, the conventional vehicle-carried navigation system shown includes a sensor apparatus 1 which in turn includes a distance sensor 11 for developing a pulse signal each time an automobile in which the vehicle-carried navigation system is incorporated runs for each predetermined distance, and a direction sensor 12 for developing a direction signal representative of an advancing direction of the vehicle.
The vehicle-carried navigation system further includes a map data storage apparatus 2 in which information for the detection of a current position of the vehicle and information for the drawing of a map are stored. The map data storage apparatus 2 may be a CD-ROM (compact disk read-only memory) in which map information is stored and a CD-ROM reproducing apparatus for reproducing such CD-ROM.
Changing over means 3 changes over the destination of map data read out from the map data storage apparatus 2 between a current position detecting apparatus 5 and a picture drawing apparatus 6 in accordance with a predetermined order of priority in response to a request or requests from one or both of the current position detecting apparatus 5 and the picture drawing apparatus 6. Each of the current position detecting apparatus 5 and the picture drawing apparatus 6 has a built-in map data memory 51 or 61 therein.
An input unit 4 has a plurality of switches not shown and scroll keys not shown for inputting therethrough data for the setting and connection of a current position, selection of a scale of a map to be displayed, selection of a region of a map to be displayed and so forth.
The current position detecting apparatus 5 detects a current position of the vehicle in accordance with a distance pulse signal and a direction signal received from the sensor apparatus 1 add map data read out from the map data storage apparatus 2 by way of the changing over means 3. The current position detecting apparatus 5 further executes setting and correction of a current position of the vehicle in accordance with a switch signal from the input unit 4.
The built-in map data memory 51 of the current position detecting apparatus 5 is provided to store therein map data read out from the map data storage apparatus 2.
The picture drawing apparatus 6 draws a map in accordance with map data read out from the map data storage apparatus 2 by way of the changing over means 3 and executes processing for the displaying of a current position on the thus drawn map in accordance with current position information received from the current position detecting means 5.
The built-in map data memory 61 of the picture drawing apparatus 6 is provided to store therein map data read out from the map data storage apparatus 2.
A display unit 7 displays a picture or a map and a current position of the vehicle thereon in response to a display signal from the picture drawing apparatus 6. The display unit 7 may be a CRT (cathode ray tube) display unit.
In operation, the current position detecting apparatus 5 executes dead-reckoning navigation in accordance with a distance pulse signal received, as the vehicle advances, from the distance sensor 11 and a direction signal received from the direction sensor 12 and representative of an advancing direction of the vehicle to calculate a new current position of the vehicle.
Meanwhile, the current position detecting apparatus 5 reads out map data from the map data storage apparatus 2 by way of the changing over means 3 and stores the map data into the map data memory 51 thereof, and then executes, in accordance with road data in the map data, map matching for the current position calculated by the dead-reckoning navigation described above to discriminate a more precise current position of the vehicle. A result of such judgment is outputted to the picture drawing apparatus 6.
Thus, the picture drawing apparatus 6 reads out, in accordance with the current position information received from the current position detecting apparatus 5, map data of a map around the current position from the map data storage apparatus 2 and stores the map data into the map data memory 61 thereof, and then executes drawing of a map in accordance with such map data.
The picture drawing apparatus 6 produces a display signal to control the display unit 7 to display thereon the map drawn by the picture drawing apparatus 6 and the current position on the thus displayed map.
Consequently, the current position of the vehicle is displayed on the display apparatus 6 together with the map around the current position.
Meanwhile, the current position 5 further executes correction of the current position and initial setting in accordance with a switch signal from the input unit 4. Similarly, the picture drawing apparatus 6 executes, in response to a switch signal from the input unit 4, drawing of a map of a different display scale or changing over of a display mode between a current position displaying mode in which a current position is displayed and another map displaying mode in which a map of an arbitrary region is displayed.
It is to be noted that, also when a map of an arbitrary region is to be displayed in the map displaying mode, the current position detecting apparatus 5 must necessarily read out map data from the map data storage apparatus 2.
In case requests for reading out of map data are received simultaneously from both of the current position detecting apparatus 5 and the picture drawing apparatus 6, a priority is provided to the current position detecting apparatus 5 by the changing over means 3 so that the current position detecting apparatus 5 reads out map data from the map data storage apparatus 2.
With the conventional vehicle-carried navigation system having such construction as described above, since the map data storage apparatus 2 is normally constituted from a CD-ROM and, a CD-ROM reproducing apparatus, a comparatively long time is required for reading out of map data, and when setting or expensive correction of a current position is performed, it is necessary for the current position detecting apparatus 5 to execute reading out of new map data, which delays judgment of a current position.
Further, when the vehicle is moving at a high speed or in some other case while the display mode is the current position displaying mode, map data must necessarily be read out frequently from both of the current position detecting apparatus 5 and the picture drawing apparatus 6, and further since a priority is provided to reading out from the current position detecting apparatus 5, updating of displaying of a map by the picture drawing apparatus 6 is delayed.
Also when the display mode is changed over from the map displaying mode to the current position displaying mode, displaying of a map around the current position is delayed.